The field of the invention is semi conductor lasers.
Multiwavelength optical sources are important components in applications such as wavelength division multiplexing, optical remote sensing, and optical data processing. Multiple wavelengths are commonly achieved from a single output by integrating the output from multiple, discrete lasers. This can lead to large and complex chip design, however. Other approaches, such as cascaded strongly gain-coupled DFB (distributed feedback) lasers, rely on the reflectivity comb from integrated multi wavelength feedback mechanisms for their operation. Such integrated design of the multi wavelength feedback makes it difficult to select and tune a wavelength while leaving other wavelength(s) unaffected.
Thus, there is a need for an improved semiconductor laser capable of dual wavelength operation. It is an object of the invention to provide such a laser.
These needs are met by the present a laser heterostructure having an active layer, a lateral waveguide terminating in an output aperture, and a gain section with a current drive electrode. A rear surface distributed Bragg grating with a tuning current electrode is formed on a surface of said laser heterostructure. The laser also includes a front surface distributed Bragg grating with a tuning current electrode on a surface of the laser heterostructure. The front surface distributed Bragg grating is closer to the output aperture than the rear surface distributed Bragg grating, There is a space between the rear surface distributed Bragg grating and the front surface distributed Bragg grating. A current drive electrode is formed on the space. Operation is best when the front surface distributed Bragg grating has adequate reflectivity at the Bragg wavelength with minimal scattering loss at other wavelengths, particularly at the wavelength of the rear surface Bragg grating.
In the present laser, dual-wavelength operation is easily achieved by biasing the gain section. A relatively low coupling coefficient, xcexa, in the front grating reduces the added cavity loss for the back grating mode. Therefore, the back grating mode reaches threshold easily. The space section lowers the current induced thermal interaction between the two uniform grating sections, significantly reducing the inadvertent wavelength drift. As a result, a tunable mode pair separations (xcex94xcex) as small as 0.3 nm and as large as 6.9 nm can be achieved.